Cataracta nuclearis is a frequently occurring eye lens cloudiness in older persons. In it the density and cloudiness of the central portion of the lens increases as the disease progresses. Parallel therewith a discoloration of the lenses from light yellow to dark brown occurs. These changes in the lens lead to a partial loss of the capacity to see or even to blindness. Despite intensive investigations, to date not much is known about the cause or the molecular mechanism of cataract formation. In Appl. Opt. 10, p.459 ff, it is described that the formation of protein aggregates with high molecular weights are responsible for lens cloudiness. The discoloration, in contrast, is attributed to the presence of photochemically induced chromophores (S. Lerman in "Altern der Linse" (Aging of the Lens), p.139 ff, Symposium ueber die Augenlinse (Symposium on the Eye Lens), Strassburg (1982)).
The diagnosis of lens cloudiness is usually made by means of a conventional slit lamp investigation. Evaluations about localization of the center of mass of the cloudiness as well as the degree of maturity of the cloudiness can hereby be made. Both evaluations are dependent to a substantial extent on subjective estimation of the condition. Up to now there has been in practice no apparatus available which can be used in routine operation for an objective determination of lens cloudiness.
Investigations of the fluorescence intensity of individual chromophores have been carried out using a modified Scheim plug camera. In this method the fluorescence is induced with a relatively wide wavelength range in the UV region (300-400 nm) and the fluorescence intensity is measured at two discrete wavelengths (440 nm and 520 nm). Unfortunately, detailed evaluations of the degree of cataracta nuclearis also cannot be made with this method.
To improve the detection sensitivity of methods for detecting minimal, but significant, changes in biological systems, various labels or tracers have been introduced in recent years. Other than radioactive labels, these are primarily fluorescence labels. All of these labels are foreign to the body and must either be injected or orally administered. Even if they are given only in trace amounts, they still adversely influence the relevant biological system.
For these reasons in recent years fluorophotometry using fluorescein as a label (Firm COHERENT) has been developed for cataract investigations. In addition to the intervention in the biological system, this method has the disadvantage that the inducing wavelength depends on the fluorescence wavelength of the fluorescein, and the patient is not permitted to subject himself to sunlight for an extended period of time after the examination since his eyes have become very light sensitive due to the fluorescein and the possibility of damage cannot be ruled out.
Fluorescein is likewise used for investigation of blood-retina and blood-water barriers or to indicate the microcapillaries of the background of the eye. Despite the above-mentioned objections, it is the accepted method since at present no better processes are available.
Since lens clouding takes place gradually, in most cases the patients in the beginning do not notice the clouding of the lenses. The physician is first sought out in a relatively advanced stage. In no event can the aforementioned methods of examination indicate an exact stage of lens clouding. Usually today four stages are used for its classification, the assignment of which by the treating physician does not always take place clearly. A substantial reason therefor lies in the fact that no quantitative values can be established for the individual stages and thus the assignment occurs subjectively and arbitrarily. For an exact determination of the course of the disease it is therefore absolutely necessary to be able to make quantitative evaluations, i.e. to establish a direct relation of the diagnostic criteria to the changes in the cataract lens. Special value must thereby be placed on early recognition in order to prevent further development of the disease or at least to delay it. The conventional slit lamp examination is much too unsensitive for this.